Physiological analyzes of synaptic mechanisms underlying the central compensation in crayfish using simultaneous intracellular recording techniques

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When the equilibrium organ of crustaceans is partially disabled, the eyestalks first take bilaterally asymmetrical posture, but they gradually recover the original symmetrical posture in a few weeks. Although this recovery process has long been known as the central compensation at the behavioral level, the physiological process subserving it largely remains unknown at the neuronal level. In this study, the synaptic mechanisms underlying the central compensation of the eyestalk posture following unilateral statolith removal have been investigated using intracellular recording and staining techniques in crayfish. Physiological analyzes of the dendritic membrane properties and synaptic activities of nonspiking giant interneurons (NGIs) that play a crucial role in the sensori-motor signal transmission for controlling the eyestalk posture revealed that not only their passive membrane properties but also the spontaneous synaptic activities showed significant changes during the compensation p … More rocess. The finding that the input resistance and membrane time constant increased or decreased after unilateral statolith removal, depending on the side of operation, clearly demonstrated that NGIs are the site of changes leading to the central compensation. However, since the spontaneous synaptic activity of NGIs reflects the spike activity of those cells that are presynaptic to NGIs, it was suggested that those presynaptic interneurons also play important roles in the central compensation. Many local interneurons that made either monosynaptic or polysynaptic connection with NGIs were identified by simultaneous intracellular recording from them. Most of these local interneurons projected dendritic branches onto the parolfactory lobe of the deutocerebrum where statocyst afferents also project directly as well as onto the protocerebrum where dendrites of NGIs are located, thus mediating statocyst information to NGIs. It is concluded that the central compensation process is based on activity changes at multiple sites in the brain including NGIs and their presynaptic cells identified in this study. Less